Developing means for electrostatic printing apparatus

ABSTRACT

Printing apparatus is disclosed in accordance with the teachings of the present invention wherein a plurality of applicators capable of retaining electrostatic developer particles are mounted in spaced relationship on movable support means such that said applicators sequentially contact an electrostatic latent image to deposit said electrostatic developer particles thereon. In an exemplary embodiment of the present invention the movable support means comprises an endless belt movable about a plurality of cylinder means.

United. States Patent [1 1 Silverberg 1 Oct. 23, 11973 DEVELOPING MEANSFOR ELECTROSTATEC PRINTING APPARATUS [75] Inventor: Morton Silverberg,Rochester, N.Y.

[73] Assignee: Xerox Corporation, Stamford,

Conn.

221 Filed: Dec. 30, 1971 211 Appl. No.: 214,111

[52] U.S. Cl ..101/1,101/DIG.13,117/17.5, 118/637, 346/74 ES [51] Int.Cl BOS b 5/00 [58] Field of Search 101/D1G. 13, 1; 118/637, DIG. 23;117/175; 346/74 ES [56] References Cited UNITED STATES PATENTS 2,890,9686/1959 Giaimo l01/D1G. 13 2,985,135 5/1961 Hickerson... 3,140,199 7/1964York 3,251,706 5/1966 Walkup 10l/D1G. 13 3,288,605 11/1966 Macklem118/637 X 3,357,349 12/1967 Decker et a1. 10l/D1G. 13 3,372,027 3/1968Gundlach et 211.. 118/637 X 3,595,208 7/1971 Koizumi 118/637 PrimaryExaminer-Edgar S. Burr Att0meyJames J. Ralabate et a1.

[57] ABSTRACT Printing apparatus is disclosed in accordance with theteachings of the present invention wherein a plurality of applicatorscapable of retaining electrostatic developer particles are mounted inspaced relationship on movable support means such that said applicatorssequentially contact an electrostatic latent image to deposit saidelectrostatic developer particles thereon. In an exemplary embodiment ofthe present invention the movable support means comprises an endlessbelt movable about a plurality of cylinder means.

5 Claims, 2 Drawing Figures DEVELOPING MEANS FOR ELECTROSTATIC PRINTINGAPPARATUS This invention relates to printing apparatus and in particularto apparatus for developing an electrostatic latent image. A descriptionof similar apparatus is disclosed in co-pending application Ser. No;214,300 filed on Dec. 30, 1971 by Howard Ring and assigned to XeroxCorporation, the assignee of the instant invention.

In the printing arts, one of the major categories of printing apparatusthat has been developed may be classified as impact printers.Conventional impact printers require hammer means to strike a selectedcharacter embodied in a character matrix, which selected character isforced into-contact with a recording medium, thereby printing acharacter. Impact printing techniques are exemplified by slow speed,shock and vibration caused by hammer movement, and excessive wear on themechanical components. Nevertheless impact printers are widely utilizedin conventional keyboard actuated printing devices such as typewriters,teletypewriters, computer read-in and read-out devices, calculatingmachines, line printers, and the like.

In recent years a new technique of printing has been developed wherein acharacter pattern of electrostatic charges is deposited upon a medium toform an electrostatic latent image which electrostatic latent image isdeveloped by the deposition of developer particles thereon. Thistechnique is embodied in the commercial process known aselectrophotography wherein the aforementioned electrostatic latent imageis produced byselectively dissipating a uniform layer of electro staticcharges by imaging modulated radiant energy thereon. Electrophotographyhas been utilized in document, reproducing machines such as thatdescribed in U .S. Pat. No. 3,301,126 which issued to R. F. Osborne etal. on Jan. 31, 19 67 and assigned to Xerox'Corporation, the assignee ofthe present invention. Electrophotography has also been utilized inphotoprinting systems such as described in U.S. Pat.,'application Ser.No. 887,666 filed. on Dec. 23, 1969. 1

The" aforementioned printing technique hasfound application in electrography systems wherein the electrostaticcharges are deposited on arecording medium by conductive, electrically biased electrodes or styli.Electrography systems have been utilized as high speed computer read-outdevices, teletypewriter receivers, facsimile receivers, and the like.

An attendant disadvantage of prior art electrostatic printing systemssuch as electrophotographic photoprinting systems and conventionalelectrography systems is the inability ofan operator to visuallyperceive a character immediately, after the recording thereof. Theapparatus heretofore utilized by the prior art for developing anelectrostatic latent'image obstructs the field of view of an operatorduring the developing process such that an entire line or a plurality oflines of images must be developed before visual examination thereof isobtained. Accordingly, an operator of a keyboard actuated electrostaticprinting device will not be cognizant of errors, such as typographicalerrors, until well after such errors are committed and the character isrecorded. The delay between the recording of information and detectingsame tends to limit the speed at which characters are recorded,resulting in inefficient operation of such electrostatic printingdevices. This has been a critical factor in attenuating enthusiasticreception of keyboard actuated electrostatic printing devices that maybe utilized as typewriters, teletypewriter transmitters, computer inputterminals, and the like.

Therefore, it is an object of the present invention to provide apparatusfor developing an electrostatic latent image. It is another object ofthe present invention to provide apparatus for recording characters on aprint receiving surface wherein each character may be visually examinedimmediately after the recording thereof.

It is a furtherobject of this invention to provide apparatus for use inan electrostatic printing device wherein a character pattern comprisedof electrostatic charges is viewed immediately after the developmentthereof.

Yet another object of this invention is to provide printing apparatusoperable at relatively high speeds which permits immediate visualdetection of a printed character.

' A still further object of the present invention is to provideapparatus for developing and viewing an electrostatic charge pattern.

, There are other objects and advantages of the invention which willbecome clear from the following detailed description of exemplaryembodiments thereof and the novel features will be particularly pointedout in connection with the appended claims.

In accordance with this invention, apparatus for developing anelectrostatic latent image is provided wherein a plurality ofapplicators capable of retaining electrostatic developer particles aremounted in spaced relationship on movable support means such that saidapplicators sequentially contact the electrostatic latent image todeposit said electrostatic developer particles thereon. An exemplaryembodiment contemplates the use of an endless belt movable about aplurality of cylinder means as a movable support means.

The present invention may be utilized with anelectrophotographic devicesuch as a document reproducing device, wherein electrostatic latentimages are formed by imaging modulated radiant energy onto a chargedsurface. The present invention may also be utilized with electrographicdevices wherein said electrostatic latent images are formed byselectively energizing electrode means disposed in the vicinity of adielectric surface. The electrostatic printing devices with which thepresent invention may be utilized are adapted to be controlled by anyconvenient source of data such as an actuatable keyboard, an originaldocument to be reproduced, a digital computer or the like.

The invention'will be more clearly understood by reference to thefollowing detailed description of exemplary embodiments thereof inconjunction with the ac-' 'companying drawings in which;

FIG. 1 is a perspective view of one embodiment of the present invention;and

FIG. 2 is a perspective view of the present invention as utilized withan electrographic device.

Referring now to the drawings wherein like reference numerals are usedthroughout, and in particular to FIG. 1, there is, illustrated aperspective view of apparatus for developing and viewing anelectrostatic latent image comprising movable support means Eli andapplicators l2 l4 and 17. Movable support means 111 comprises an endlessbelt deployed about cylinder means t5 and 16 and movable in thedirection indicated by the arrow A. Accordingly, a source of motivepower, not shown, may be provided to drive cylinder means and 16. Theapplicators, four of which are identified by reference characters l2,l3, lid and ll'i', are mounted on the surface of endless belt ill bysuitable fastening means such as cement. Each of applicators l2, l3, l4and l7 is capable of retaining conven tional electrostatic developerparticles that may be applied thereto. Such electrostatic developerparticles are known as toner particles and are adapted to exhibit anelectrostatic charge. The toner particles may exhibit a positive ornegative charge for a purpose soon to be described. Those of ordinaryskill in the art will recognize that such toner particles may consist ofa pigmented resinous powder. Alternatively the toner particles may bedispersed in an insulating liquid.

The applicators l2, l3, l4 and ll? are preferably comprised of fibrousbrushes which may be made from materials such as natural fur (beaver,rabbit or the like) or other materials described in U.S. Pat. No.3,251,706 which issued to L. E. Walkup on May 17, 1966 and assigned toXerox Corporation. l-ience, triboelectric attraction is maintainedbetween the applicators and the electrostatic developer particles. Theapplicators are mounted such that substantially equal spaces are definedbetween successive applicators. The particular shape of each applicatoris not critical per se; however, it is desirable that the fibersincluded in each applicator extend in a direction parallel to thesurface of endless belt l 1 such that the terminal points of the fibersdefine a plane substantially perpendicular to the surface of the endlessbelt M. It is noted that the fibers must be capable of engaging inintimate contact with an electrostatic latent image to be developed.Accordingly, applicator 12 includes fibers ll2ll extending from thesurface 122 of the applicator. Similarly applicator 13 includes fibersll3ll extending from the surface H32 of the applicator. Hence, eachapplicator has a working, or operating, surface that is substantiallynormal to the surface of endless belt ill.

The developing apparatus illustrated in FIG. 1 is adapted to be suppliedwith electrostatic developer particles and to deposit said particles onan electrostatic charge pattern to thereby produce a visible image. Theelectrostatic charge pattern may be carried by a suitable printreceiving surface such as a conventional electrophotographic member oran insulating recording medium to be described in detail below.

in operation, the applicators are transported to a source ofelectrostatic developer particles, which source may be located forexample in the vicinity of the lower portion of the endless belt ill.The electrostatic developer particles supplied by the source areretained by the fibers of each applicator in accordance withtriboelectric attraction. The applicator thus loaded with electrostaticdeveloper particles are transported to the upper portion of endless beltlll whereupon the fibers or operating surface of the applicatorslinearly scan the surface of a print receiving surface. When the fiberscontact an electrostatic charge pattern the electrostatic developerparticles retained by the applicators are removed therefrom anddeposited on the charge pattern. it is understood that successivetraversals of the electrostatic charge pattern by the applicatorsmounted on endless belt lll tend to ensure an adequately developedimage. After sweeping across a line on the print receiving surface, theapplicators are again transported to the source of electrostaticdeveloper particles whereat they are resupplied with developerparticles.

It is recognized that when an applicator sweeps over an electrostaticlatent image the visible image developed thereby may be immediatelyobserved along an optical path, designated by the arrow B, which passesthrough the space defined by two successive applicators. The opticalpath will be interrupted by the next successive applicator transportedtherepast by the endless belt llll. Accordingly, a flickering effect isintroduced to the visual observation of a recorded character.Nevertheless the transport velocity of endless belt ill, the spatialseparation between successive applicators and the width of eachapplicator may be particularly selected such that the flickering effectis not readily noticeable by an observer. Thus, if a print receivingsurface is disposed in a plane above the plane of the drawings and anobserver is positioned in a plane beneath the plane of the drawings eachapplicator traverses an entire line on the print receiving surface todevelop electrostatic charge patterns deposited on said line, and theobserver may view each of the characters immediately after thedevelopment thereof. it is of course recognized that the distancebetween the longitudinal axes of cylinder means 15 and 16 isdeterminative of the length of the line developed. One of ordinary skillin the art will understand that although two cylinder means l5 and 16,about which the endless belt ill is deployed are illustrated herein, anyconvenient number of cylinder means may be utilized such that theendless belt it assumes a corresponding geometric configuration such astriangular, rectangular or the like.

Referring now to FIG. 2 there is illustrated one embodiment of thepresent invention which may be utilized in an electrostatic printingdevice, and comprises the apparatus of FlG. ll including endless beltill and applicators 12-14 and 17, insulating recording medium Zll,electrode means 22, electrographic stylus 2d, and a source of motivepower 30. The endless belt ill is understood to be a continuousstructure; however to facilitate the explanation of the applicability ofthe present invention to an electrostatic printing device the endlessbelt M is diagrammatically illustrated in broken configuration. Theinsulating recording medium IZll may be comprised of a base paper whichis electrically conduc tive and which is coated with a dielectricalplastic having a very high resistivity. Alternatively, the insulatingrecording medium may comprise any other dielectric sheet having asufficiently high resistance to retain an electrostatic charge pattern.The insulating recording medium 21 is supported by electrode means 21and guide support member 2? and is adapted to be advanced in thedirection indicated by the arrow B. Electrode means 22 serves as a baseelectrode and supports the insulating recording medium Ell in closeproximity to the electrographic stylus 2d.

Electrode means 22 includes a surface portion 221 adapted to maintainthe insulating recording medium Ell in a plane parallel to the surfaceof electrographic stylus 2d and perpendicular to the longitudinal axesof cylinder means and 116.

The electrographic stylus Ltd may include a matrix array of parallelconductive electrodes suitably isolated electrically from each other.The matrix array of conductive electrodes may be pin electrodessupported by insulating support means 25 through which electrical Sconductors maybe provided to each of'the pin electrodes for theselective energization thereof in response to electrical recordingsignals. The electrical signals supplied to the conductors may begenerated by the actuation of a keyboard, by the receipt of facsimilesignals, or by any suitable source of data signals. lnsulating supportmeans 25 is adapted to support the electrographic stylus 24 at asuitable distance from the insulating recording medium 21 such that airionization may occur in the air gap between the electrographic stylus 24and the surface of the insulating recording means 21, whereby a smallelectrical discharge may be established between the selectivelyenergized electrodes and the electrode means 22. Suitable distances thathave heretofore been utilized are within the range three to fivethousandths of an inch between the electrodes. I

To facilitate the recording of a line of characters, relative lateraldisplacement must exist between the insulating recording medium 21 andthe electrographic stylus 24. Accordingly, insulating support means 25may be displaced by a suitable motor, not shown, which may be a constantdrive motor or a conventional stepping motor. Additional means may beprovided for returning the insulating support means 25 from a rightmostposition to a leftmost position after. the recording of a complete lineof characters. One example of suitable drive means is described in U.S.Pat. application Ser. No. 805,694 filed on Mar.- 10, 1969, and assignedto Xerox Corporation. Alternatively, the insulating support means 25 mayremain fixed, and electrode means 22 and guide support member 23 mayform a conventional movable carriage adapted to transport the insulatingrecording medium 21 in a right to left direction, thereby enabling theelectrographic stylus 24 to record successive characters thereon.

The endless belt 11 is positionedsuch that the operating surface. ofeach of applicators 12, 13 and 14 and 17 mounted thereon may travel intocontact with the surface of the insulating recording medium 21. Hence,the insulating recording medium may be disposed in. the plane defined bythe terminal points of the fibers of the .applicatorsfThe electrographicstylus 24 is interposed between theinsulating recording medium 21 andthe endless belt 11. It is understood however, thatwhen. the applicators12-14 travel into the vicinity of the electrographic stylus 24 thefibers of each of the applicators are deformed by the insulating supportmeans 25 to permit displacement therepast, and no interaction occursbetween. the charged electrostatic developer particles retained by theapplicators and the electrodes included in the electrographic stylus. Ashaft 26 is suitably fastened to one of the cylinders 16 and is supplieda with a rotationaltorque by the source of motive power 30. The sourceof motive power3tl may comprise a conventional electric motor which maybe a constant drive motor or a conventional stepping motor. Conv'en-'tionalcoupling means comprised of endless belt 2'7 deployed aboutrollers 28 and 29 may be utilized to couple the motor 30 tothe shaft 26.Other mechanical coupling means such as drive speed reducing gears maybe utilized if desired. It is preferable that the rotational speed ofelectric motor 30 be maintained at a-constant value notwithstanding theloading effects produced when an applicator travels into the vicinity ofinsulating support means 25.

Although not illustrated in FllG. 2 it is understood that a source ofelectrostatic developer particles is provided to supply the applicators12-14 and 117 with electrostatic developer particles subsequent to thedeposition of such particles upon an electrostatic charge pattern. Thesource of electrostatic developer particles may be similar to thatdescribed in the aforementioned US. Pat. Application Serial No. 805,694or may comprise suitable liquid dispersion apparatus well known to thoseof ordinary skill in the art.

The operation of the electrographic recording device illustrated in FIG.2 incorporating the present invention will now be described. Electricmotor 30 imparts a velocity to the endless belt 11 such that the endlessbelt is displaced in the direction indicated by the arrow A.Electrostatic developer particles are applied to each of applicators12-14 and 17 by a source of particles not shown. The fibers included ineach of the applicators serve to charge the supplied electrostaticdeveloper particles whereby the particles are retained by triboelectricattraction to the applicators. Electrostatic developer particles will besupplied to those applicators and portions of applicators which aredeficient in particles. Consequently, the consideration of non-uniformloading of an applicator, i.e., excess electrostatic developer particlessupplied to an applicator, is obviated.

Electrographic stylus 24 is proximately situated with respect tothedielectric coating of insulating recording means 21 and the conductingsurface of insulating recording means 21 is an intimate contact with thesurface 221 of electrode 22. The electrographic stylus 24 is selectivelyenergized by applying data signals thereto such as by depressing aselected key of a keyboard, by supplying received facsimile signalsthereto, or the like.

The selective energization of electrographic stylus 24 establishescorresponding electrical discharges between each of theselectively'energized electrodes included in the electrographic stylus2d and electrode means 22. Accordingly, ions which are created in theair gap between the electrographic stylus 24 and the surface ofinsulating recording means 21 are deposited on the surface of theinsulating recording means 21 in a patterncorresponding to theselectively energized electrodes. Thus an electrostatic latent imagecomprised of an electrostatic charge pattern is formed. The.

polarity of the electrostatic charge pattern may be positive ornegative, however itshould be noted that said polarityshould be oppositeto that of the electrostatic developer particles retained by theapplicators 12-14 and 17. After forming an electrostatic latent imagethe electrographic stylus 24 supported by insulating support means 25 isdisplaced a suitable amount in preparation for the recording of asubsequent image. The direction of displacement may be in correspondencewith or opposite to the direction of travel of the illustratedapplicators.Alternatively the carriage assembly comprised of electrodemeans 22 and guide support means 23 may bedisplaced to prepare theinsulating recording means 21 for reception of a subsequentelectrostatic latent image. i

The electrostatic latent image formed on insulating recording means 21is developed to form a visible image when one of applicators 12-14 and17 travels a into contact therewith. Itshould be understood that when anapplicator sweeps over an electrostatic charge pattern the electrostaticforce exerted on the electrostatic developer particles is sufficient toovercome the triboelectric attraction between the developer particlesand the fibers of the applicator to thereby urge the particles intocontact with the charge pattern. It may be observed that the forcesexerted on the electrostatic developer particles by the impact betweenan applicator and the surface of the insulating recording means 21 maybe sufficient to dislodge said particles from the applicator. Theelectrostatic developer particles however, will be attracted only to anelectrostatic charge pattern. Thus, if the insulating recording means 21sup ports a developed image, or if an electrostatic latent image is notpresent the dislodged electrostatic developer particles will merelycascade across the surface of the insulating recording medium 211 to berecovered by a sump located beneath the illustrated apparatus. Thus inaccordance with the configuration illustrated in W0. 2 if the charactersC, D" and E have been previously developed and the character F is anelectrostatic charge pattern deposited on the surface of the insulatingrecording medium 211 by selectively energized electrographic stylus 2d,electrostatic developer particles retained by the fibers of applicator112 will be removed therefrom to develop the image of the character F.Other electrostatic developer particles will be removed from applicator112 in the vicinity of the developed images of characters C, D and E".However, insufficient electrostatic forces will exist between thedeveloped images and said other removed electrostatic developerparticles, and the electrostatic developer particles will fall, underthe influence of the gravitational forces exerted thereon, to a sump forsubsequent recovery thereof. One of ordinary skill in the art willrecognize that each of the applicators 1241 5 and 17 will successivelyscan a line of insulating recording means 21 to deposit theelectrostatic developer particles retained thereby onto theelectrostatic charge patterns formed by the electrographic stylus 2d. itshould be noted that electrographic stylus 2d may be aligned with eitherthe upper half of the endless belt it or with the lower half thereof. Inaddition, successive portions of the fibers of each applicator will bedeformed by the presence of the insulating support means 25 as-each application is displaced. Thus each applicator is subjected to uniformwear. along the entire length thereof It may now be seen that an opticalpath may be established from an observer to a developed image throughthe space defined by adjacent applicators. The observer may be theoperator of a keyboard adapted to be utilized with the apparatusillustrated in FIG. 2. Thus, each character may be perceived immediatelyafter the recording thereof and it is not necessary to record a rplurality of lines of characters before observation of a first recordedline of characters is obtained. One advantage of mounting a plurality ofapplicators on the endless belt 111 is that improved development ofelectrostatic images obtains. For example if the character 13" is notadequately developed by the deposition of electrostatic developerparticles thereon by the applicator 112, additional electrostaticdeveloper particles may be deposited thereon by applicators lid andilili until a suitably developed image is obtained. Althoughsatisfactory development of a recorded electrostatic latent image may berealized by a multiplicity of applicators mounted on the endless belt M,it is appreciated that the flickering effect by which an observer mayperceive the recorded characters may become objectionably noticeable itan inordinate amount of applicators is utilized.

After development, the electrostatic developer particles may be fixed tothe insulating recording medium 211 in any of several conventionalmanners. For example, guide support means 23 may include a conventionalheating assembly through which the insulating recording medium 21 isadvanced. The heating assembly may fuse the electrostatic developerparticles to the surface of the insulating recording medium 211 in thewell-known manner. Flash fusing or fixing may also be used to render thedeveloped images permanent.

It should be recognized by those of ordinary skill in the art that theelectrostatic charge patterns may be deposited on the surface of theinsulating recording medium 2 by conventional means other than theelectrographic stylus 2d illustrated herein. For example, a linear arrayof energizable light emissive elements may be disposed to selectivelydissipate a uniform layer of electrostatic charge deposited on thesurface of the insulating recording medium 21. The insulating recordingmedium may comprise a conventional electrophotographic member and thelinear array of light emissive elements may be selectively energized inaccordance with data signals supplied thereto. in addition the lightemissive elements may be positioned in a manner that does not interferewith the optical path established between an observer and a recordedcharacter, which optical path passes through the space defined byadjacent applicators.

While the invention has been particularly shown and described withreference to exemplary embodiments thereof it will be obvious to thoseof ordinary skill in the art that the foregoing and various otherchanges and modifications in form and details may be made withoutdeparting from the spirit and scope of the in vention. It is thereforeintended that the appended claims be interpreted as including all suchchanges and modifications.

What is claimed is:

.11. Apparatus for developing an electrostatic latent image, comprisingan endless belt movable about a plurality of cylinder means, and aplurality of applicators capable of retaining electrostatic developerparticles, said applicators comprising fibrous brushes each of whichincludes fibers extending in a direction parallel to the surface of saidendless belt such that the terminal points of said fibers define a planeperpendicular to said surface of said endless belt and said plurality ofapplicators being mounted in spaced relationship on said endless beltsuchthat said applicators successively contact said electrostatic latentimage to deposit electrostatic developer particles thereon, andperiodically interrupt an optical path to a developed imagewhen anapplicator traverses said optical path.

2. Apparatus for printing characters on a print receiving surface,comprising:

means for forming characters comprised of electrostatic charge patternson said print receiving surface;

an endless belt having a surface movable in a plane applicator meanshaving a surface thereof substantially normal to said endless beltsurface for successively contacting said print receiving surface todeface of said endless belt, said plurality of applicators being mountedin spaced relationship on said endless belt such that said applicatorssuccessively posit electrostatic developer particles'on saidelectrostatic charge patterns and for periodically interrupting anoptical path to a printed character.

3. Apparatus for printing characters on a print receiving surface,comprising:

means for forming characters comprised of electrostatic charge patternson said print receiving sur- 10 face;

an endless belt having a surface movable in a plane normal to said printreceiving surface and deployed about a plurality of cylinder means, saidcylinder means having their respective longitudinal axes disposed inperpendicular relationship with respect to said print receiving surface;and

a plurality of applicators capable of retaining electrostatic developerparticles, said applicators comprising fibrous brushes each of whichincludes fibers contact said print receiving surface to depositelectrostatic developer particles on said electrostatic charge patternsand periodically interrupt an optical path to a printed character.

4. The apparatus of claim 3 wherein said at least two longitudinal axesare spaced apart a distance corresponding to the lateral dimension ofsaid print receiving surface.

5. The apparatus of claim 4 wherein said means for forming characterscomprised of electrostatic charge patterns comprises stylus meansinterposed between said endless belt and said print receiving surfaceand adapted for relative lateral displacement with respect to said printreceiving surface; said stylus means being responsive to the selectiveenergization thereof to deposit an electrostatic charge pattern on saidprint reextending in a direction parallel to the s rfa e of ceivingsurface in accordance with said selective enersaid endless belt suchthat the terminal points of gization. said fibers define a planeperpendicular to said sur-

1. Apparatus for developing an electrostatic latent image, comprisinG an endless belt movable about a plurality of cylinder means, and a plurality of applicators capable of retaining electrostatic developer particles, said applicators comprising fibrous brushes each of which includes fibers extending in a direction parallel to the surface of said endless belt such that the terminal points of said fibers define a plane perpendicular to said surface of said endless belt and said plurality of applicators being mounted in spaced relationship on said endless belt such that said applicators successively contact said electrostatic latent image to deposit electrostatic developer particles thereon, and periodically interrupt an optical path to a developed image when an applicator traverses said optical path.
 2. Apparatus for printing characters on a print receiving surface, comprising: means for forming characters comprised of electrostatic charge patterns on said print receiving surface; an endless belt having a surface movable in a plane normal to said print receiving surface and deployed about a plurality of cylinder means, said cylinder means having their respective longitudinal axes disposed in perpendicular relationship with respect to said print receiving surface; and a plurality of applicator means capable of retaining electrostatic developer particles and mounted in spaced relationship on said endless belt, each said applicator means having a surface thereof substantially normal to said endless belt surface for successively contacting said print receiving surface to deposit electrostatic developer particles on said electrostatic charge patterns and for periodically interrupting an optical path to a printed character.
 3. Apparatus for printing characters on a print receiving surface, comprising: means for forming characters comprised of electrostatic charge patterns on said print receiving surface; an endless belt having a surface movable in a plane normal to said print receiving surface and deployed about a plurality of cylinder means, said cylinder means having their respective longitudinal axes disposed in perpendicular relationship with respect to said print receiving surface; and a plurality of applicators capable of retaining electrostatic developer particles, said applicators comprising fibrous brushes each of which includes fibers extending in a direction parallel to the surface of said endless belt such that the terminal points of said fibers define a plane perpendicular to said surface of said endless belt, said plurality of applicators being mounted in spaced relationship on said endless belt such that said applicators successively contact said print receiving surface to deposit electrostatic developer particles on said electrostatic charge patterns and periodically interrupt an optical path to a printed character.
 4. The apparatus of claim 3 wherein said at least two longitudinal axes are spaced apart a distance corresponding to the lateral dimension of said print receiving surface.
 5. The apparatus of claim 4 wherein said means for forming characters comprised of electrostatic charge patterns comprises stylus means interposed between said endless belt and said print receiving surface and adapted for relative lateral displacement with respect to said print receiving surface; said stylus means being responsive to the selective energization thereof to deposit an electrostatic charge pattern on said print receiving surface in accordance with said selective energization. 